This invention relates to a process for the preparation of diacyl peroxide compositions having improved properties.
Diacyl peroxides are organic compounds, which find industrial application in the most varied areas, particularly in polymerization and oxidation reactions. Another very important area of application for such organic peroxides is the curing of unsaturated polyester resins. The organic peroxides may also be used in the preparation of acrylic resins.
Since pure organic diacyl peroxides are relatively unstable and tend to decompose, or even to disintegrate explosively, there have been numerous attempts to stabilize the peroxides and make them less dangerous to handle, so that they may be transported without extensive risk. Is is therefore known to mix organic peroxides with desensitizing agents. For example, customary desensitizing agents for organic peroxides are esters of phthalic acid, such as dioctyl phthalate, phosphoric esters, silicone oils, or chlorinated paraffins. The stabilized peroxides may be made up in the form of a solution, a paste, a dispersion, granules, or powder. The known dispersions and pastes are afflicted with the disadvantage that there may be demixing, so that the activity of the preparation is not uniform. Thus, heterogeneities may form due to settling and demixing, so that in the case of a product in a container, the upper layers may have different characteristics than those in the middle, or the lower portion of the container. However, industrial applications require a product of uniform quality.
Peroxides supplied in the form of dry powders show a tendency for dust formation and are also more impact-sensitive than material which is in the form of a paste. Solutions of mixed peroxides in esters of phthalic acid are described in U.S. Pat. No. 2,454,254. Among other things, a disadvantage of the process therein described is that the peroxide must first be prepared in a separate operation. Also, to prepare a stable solution, the peroxide must first be dried.
German Pat. No. 1,256,644, as well as German Patent Disclosure No. 1,768,199 describe processes for the preparation of anhydrous granules of organic peroxides through treatment of water-containing organic peroxides with desensitizing agents. Thereby, the water-containing crude peroxide has to be dispersed in at least 10 times the quantity of water. Instead of the crude peroxide dispersion one may also use the carboxylic chloride and hydrogen peroxide, which are required for its preparation, in an alkaline aqueous phase. Aside from the fact that working with such large quantities of water is cumbersome and attended by disadvantages, the product must later be made anhydrous. In addition, according to the processes pursuant to these two publications, attention must be paid to careful continuation of the solid components, so that frequently the use of special equipment, such as rollers, colloid mills, and the like, becomes unavoidable. Furthermore, the addition of organic solvents, such as benzene, is usually required. Furthermore, no pastes are obtained according to the teachings of the foregoing publications.
Finally, U.S. Pat. No. 3,538,011 describes the preparation of stabilized, anhydrous peroxide compositions, in which a softening agent with a melting point of more than 40.degree. C. is used. The products described therein are obtained as granules or powder.
Although numerous processes for the preparation of stabilized peroxide mixtures of the most varied compositions have previously been described, there is still a need for a simpler, economical preparation method, resulting in products with improved characteristics.
It is therefore a purpose of this invention, to make available an especially simple, rapid, and economic process for the preparation of pastes containing diacyl peroxides. Another goal of the invention is a process for the preparation of such pastes having a low content of undesirable additives, such as chlorides. An additional goal of the invention is the preparation of storable pastes that are especially stable, do not have to be completely dried for purposes of storing and have little or no tendency to demix. It is furthermore a goal of the invention to prepare peroxide pastes which display an especially favorable crystal structure. It is still another purpose of the invention to provide peroxide pastes which may be blended with customary additives, such as pigments and other desirable additives without leading to premature decomposition. A final object of the present invention is to provide a process for the preparation of peroxide pastes which rapidly dissolve in unsaturated polyester resins.